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Bob uk
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Posted on Monday, 30 June, 2014 - 08:03 am:   Edit PostDelete PostView Post/Check IP

RR call these brake distribution valves

The early type had 4 ports

The later ones 3 ports

The 3 ports are pressure in
Pressure out and return

The 4th port is for a bleed nipple which was deleted on the later ones

Return is aka dump

When the brakes are off the dump is connected to out let port and the calipers and no dot flows through the valve

When the brakes are on the inlet is connected to the outlet and the dump is shut off and dot moves through the valve

When the brake is released the inlet port is shut off and the pressure in the outlet moves the dot into the dump and back to tank


The line between the brake valve and the accumulator is under pressure this will squeeze any air to about 1 200th of its volume

If the brake is pumped down then as a full accumulator load of dot flows through the valve taking the air with it

Open the caliper bleeders and bleed off egg cup full and that bit of the circuit is fully bled

The valve spool is held off by a spring and hydraulic pressure which gives a modicum of feel

The valve relies on that the clearance between spool and bore is small enough to contain the molecules of dot leaking out

And a seal at the front in the bore

The out dust cover is only a dust cover

The dot is allowed to seep along the clearance to lubricate the valve

A small drip from the valve is normal

The spools are not interchangeable

As normal when overhauling don't scratch any thing

To polish the bore or spool use Worn 1200 or finer with dot as lubrication

Only polish if needed and little as possible

Clean in meths

These valves are very reliable and last well so if there is a fault look at valves last

Next the tank

(Message approved by david_gore)
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Bob uk
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Posted on Wednesday, 20 August, 2014 - 11:03 am:   Edit PostDelete PostView Post/Check IP

Any more information needed just ask.

(Message approved by david_gore)
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Bob UK
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Posted on Thursday, 21 August, 2014 - 06:16 am:   Edit PostDelete PostView Post/Check IP

Since writing the above.
Spool valves are made by machining a body with every thing finished except the bore which would be left 2 thou undersize.
Position of ports has
tolerance of 0.001"
Then the bore is honed to 0.0001" tolerance.

Then the spool would be made to finish size complete with grooves.
the diameter has a tolerance of 0.0001
The width and position the grooves , tolerance 0.001.
Depth of grooves 0.005 tolerance.

A spool than is 0.0001 small and a bore that is 0.0001 won't fit and would stick and rip the surfaces up.

A pair that are both 0.0001" Will do the same. Interchange them and the clearance will be 0.0002 Which will leak.

To machine that tighter tolerance is a feat of engineering plus to measure it the bits have to be at 20 centigrade.

So make say a hundred pairs and hand match.

On something with O rings a 0.001 tolerance would apply. And sometimes a bit will be 0.0001 - 0.0004 say.

A good machine will hold 0.002" on the dials. Grinders Will hold a 0.001". A digital read out, will tighten the accuracy to 0.001 on a mill or lathe and 0.0002 on a grinder.

I can't get closer than 0.0005 And even then I scrap a few. Once in a while with the wind in the right direction I get to 0.0001

Not only that it has to be parallel. So that rules out 2000 grit and polish.

And a very very fine finish is required.
600 is cheap.

(Message approved by david_gore)

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